Yūji Yagami is a high school student with an unusual problem. His mother, Nomi, is abnormally youthful in both her looks and mannerisms and Yūji has developed a crush on her. Nomi however, is oblivious to Yūji's Oedipus complex and unknowingly tempts him with her overly-passionate displays of affections to both her husband and son. The situation is further complicated when Yūji receives a love letter on Valentine's Day.